Film structures are widely used for various purposes through surface contact with other objects. Such purposes include wrapping, binding, fastening, sealing and dispensing chemical agents. An operating surface of a film structure may carry an operating agent having a certain operating effect on a target object when the operating agent and the surface of the target object contact each other. One of the most common examples of such film structures is a sheet material having an adhesive operating agent. When the adhesive side is applied on a surface of another object, the sheet material sticks to the contacting surface of the object, forming a bond. Another example is a sheet material having a carrier side containing a chemical or a drug. When the carrier side contacts a surface of an object, the agent (a chemical or a drug) is dispensed to the target surface to take effect on the surface.
In the above described applications, often a user wishes to have control over when, where, how, which part of the film and to what degree the intended operating effect is applied. Traditional film structures do not offer such convenient features. For example, in the art of tapes, labels, and other articles using pressure-sensitive adhesive (PSA) to adhere an adhesive coated surface to a target surface, premature adhesion sometimes is a problem. That is, before the adhesive coated surface can be properly positioned over the target surface, inadvertent contact of the adhesive with the target surface causes premature adhesion at one or more locations, thereby inhibiting proper positioning. Additionally, inadvertent contact between different parts of the same adhesive coated surface can also create problems and waste. Pressure-sensitive adhesive sheet structures (composed of a substrate such as a film or sheet and a pressure sensitive adhesive layer formed on its surface) for example, are employed in a wide range of applications such as signboards, decorative and display applications in automobiles, buildings and containers. Such pressure-sensitive adhesive layers have very high initial adhesion strength, making the adhesion highly uncontrollable. Where the precise positioning of the film structure is required, even skilled workmen experience difficulty in accurately bonding such a pressure sensitive adhesive layer to the desired site in one operation, and removal from the desired site is often necessary. But with a traditional pressure-sensitive adhesive, once the initial contact is made, it is difficult to adjust the position of the film structure.
Another example where more user control is desired is found in thin films commonly used to wrap food. Most commercial food wraps undesirably “cling” to themselves when they are dispensed. Such undesirable properties make the application of the film difficult to control.
Others have attempted to overcome the above described problem of lacking user control. U.S. Pat. No. 5,965,235 to McGuire et al., for example, discloses a three-dimensional sheet material having an application side from which a plurality of spaced three-dimensional protrusions extend outwardly. The protrusions are separated by an interconnected network of three-dimensional spaces between adjacent protrusions. The sheet structure disclosed in McGuire et al. is designed to resist nesting of superimposed layers into one another. The three-dimensional, nesting-resistant sheet materials are manufactured utilizing a three-dimensional forming structure comprising an amorphous pattern of spaced three-dimensional recesses separated by interconnected lands. To manufacture the three-dimensional, nest-resistant sheet materials, a sheet of the formable material is introduced onto the forming structure and permanently deformed into compliance with the forming structure.
PCT Patent WO 97/25268 discloses a substance (such as a drug) delivery system having a three-dimensional structure with outer-most surface features and spaces for containing a substance. The substance has a level below the outermost surface features such that the substance is protected from inadvertent contact with the external surface. The substance remains protected until the three-dimensional structure is sufficiently deformed into the substantially two-dimensional structure and the substances thereby exposed to contact an external surface without compliance of the external surface being necessary. The manufacture of the three-dimensional material includes the steps of coating a substance onto a forming surface, transferring the coating of substance from the forming surface to a piece of material, and forming the piece of material into a three-dimensional structure on the forming surface while the substance is in contact with the forming surface.
A three-dimensional sheet structure similar to that of PCT Patent WO 97/25268 is disclosed in PCT Patent WO 98/55109, in which the sheet structure further provides a selectively-activatible sheet material for dispensing and dispersing a substance (i.e., a drug) onto the target surface. The application side of the sheet material has a plurality of hollow protrusions extending outwardly and separate from one another by valleys, while the opposite side has a plurality of depressions corresponding with the hollow provisions. A substance adheres to and partially fills a location protected from external contact comprising the valleys and/or the depressions. The sheet material may be selectively activated by deforming the hollow progressions to deliver the substance to the target surface.
U.S. Pat. No. 5,240,761 to Calhoun et al. discloses a method of separating a dense monolayer of electrically conductive particles covering an adhesive layer by stretching the adhesive layer. The resultant film has a removable backing layer, and with the backing layer removed, can be used to electrically connect two substrates having electrically conductive elements.
Due to the importance of three-dimensional film structures having controllable contact properties, it is desirable to develop less expensive and more efficient methods of making such film structures, and to provide alternative film structures suitable for a variety of applications.